A variety of tools and methods are available for extracting information from electronic devices by sensing their internal signals. These tools and methods may be used by hackers to gain unauthorized access to secret information within such devices. In response, device manufacturers have developed techniques for impeding such attacks.
For example, U.S. Patent Application Publication 2005/0002523, whose disclosure is incorporated herein by reference, describes an apparatus is said to provide security against differential power analysis (DPA) attacks. The apparatus has a multiplexer with a control input, data inputs, and a data output for the encrypted mapped output value for through-connecting an encrypted data signal at one of the data inputs to the data output. The encrypted data signals for the data inputs of the multiplexer are provided based on an encryption key. A control signal indicating the output value to be mapped is applied to the control input of the multiplexer.
U.S. Pat. No. 7,420,862, whose disclosure is incorporated herein by reference, describes a data inversion device, which includes a differential amplifier having first and second input lines. A controller is coupled to selectively and individually decouple the first and second input lines from the differential amplifier.
PCT International Publication WO 2009/156881, whose disclosure is incorporated herein by reference, describes a method for hindering detection of information unintentionally leaked from a secret held in a memory unit. The memory unit is in a non-operational state during at least a first amount of time, after which a condition under which the memory unit operates changes, thereby causing the memory unit to enter an operational state. After waiting for a second amount of time, at least a second condition under which the memory unit operates is changed, thereby causing the memory unit to enter the non-operational state. Access to the secret information is enabled only during the second amount of time, and detection of secret information unintentionally leaked is limited during the first amount of time.